Tools for Practice
Screening and diagnosis of type 2 diabetes with HbA1c Marco Mannarino
MD CCFP
Marcello Tonelli
MD SM FRCPC
G. Michael Allan
Clinical question Is hemoglobin A1c (HbA1c) testing appropriate for screening and diagnosis of type 2 diabetes mellitus?
Evidence •
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Agreement between HbA1c and fasting plasma glucose (FPG) or oral glucose tolerance testing (OGTT) is poor: -25% to 27% agreement for HbA1c and FPG1,2; -22% to 33% agreement for HbA1c and OGTT.1,3,4 Some studies find HbA1c (≥ 6.5%) would diagnose less diabetes than OGTT1,5,6 (eg, HbA1c missed 60% of the cases OGTT diagnosed6); some find HbA1c (≥ 6.5%) would diagnose more diabetes than OGTT2-5 (eg, OGTT missed 35% of the cases HbA1c diagnosed4). In predicting outcomes of diabetes, HbA1c -performs as well as and often better than FPG7-10 and -might be similar to OGTT, but evidence is lacking7,9; HbA1c levels for best prediction vary by study.7-10 Using a diagnostic cutoff of HbA1c ≥ 6.5%: -Higher HbA1c improves specificity; lower improves sensitivity. -One study found HbA1c of ≥ 6.5% had a sensitivity and specificity of 44% and 79%, respectively.11 -While some data suggest the cutoff could be lower,12-14 consistency is lacking,5 and racial differences do exist.15
Context •
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Although FPG has been the preferred diagnostic test for diabetes for years, it requires patient compliance with fasting and has high intraindividual variability.7,16 Agreement between FPG and OGTT is also poor.17,18 HbA1c is more expensive and not reliable in certain conditions (eg, hemoglobinopathies),19 but does not require fasting and has less intraindividual variability than FPG.7 Recent American,20 WHO,21 and Canadian Task Force on Preventive Health Care (CTFPHC)22 recommendations include HbA1c of ≥ 6.5% for screening and diagnosis. -Screening and diagnostic tests are the same in diabetes.20 -Positive results (FPG, OGTT, or HbA1c) should be confirmed with repeat testing using the same test.20
Bottom line An HbA1c cutoff of ≥ 6.5% can be used to screen for and diagnose type 2 diabetes. Controversy persists around appropriate cutoffs and agreement with other tests.
Implementation There is no evidence that screening adults at low or moderate risk of diabetes will improve outcomes; low-quality evidence suggests that screening high-risk adults could reduce complications.22 The CTFPHC recently published new
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Canadian Family Physician • Le Médecin de famille canadien
MD CCFP
guidance on screening for diabetes, identifying HbA1c as the preferred test. The CTFPHC recommends using a validated risk calculator (preferably FINDRISC23) to identify adults at high or very high risk. High-risk adults should be screened with HbA1c every 3 to 5 years; those at very high risk should be screened annually. FINDRISC23 requires consideration of diet, exercise, and body weight, so using these risk calculators offers opportunities to discuss other risk factors. Dr Mannarino is a family doctor in Edmonton, Alta. Dr Tonelli is Professor in the Division of Nephrology and Chair of the Canadian Task Force on Preventive Health Care, and Dr Allan is Associate Professor in the Department of Family Medicine, both at the University of Alberta in Edmonton. The opinions expressed in this Tools for Practice article are those of the authors and do not necessarily mirror the perspective and policy of the Alberta College of Family Physicians. References 1. Farhan S, Jarai R, Tentzeris I, Kautzky-Willer A, Samaha E, Smetana P, et al. Comparison of HbA1c and oral glucose tolerance test for diagnosis of diabetes in patients with coronary artery disease. Clin Res Cardiol 2012;101(8):625-30. 2. Bernal-Lopez MR, Santamaría-Fernandez S, Lopez-Carmona D, Tinahones FJ, Mancera-Romero J, Peña-Jimenez D, et al. HbA(1c) in adults without known diabetes from southern Europe. Impact of the new diagnostic criteria in clinical practice. Diabet Med 2011;28(11):1319-22. 3. Cosson E, Nguyen MT, Hamo-Tchatchouang E, Banu I, Chiheb S, Charnaux N, et al. What would be the outcome if the American Diabetes Association recommendations of 2010 had been followed in our practice in 1998-2006? Diabet Med 2011;28(5):567-74. 4. Mostafa SA, Davies MJ, Webb D, Gray LJ, Srinivasan BT, Jarvis J, et al. The potential impact of using glycated haemoglobin as the preferred diagnostic tool for detecting type 2 diabetes mellitus. Diabet Med 2010;27(7):762-9. 5. Malkani S, Mordes JP. Implications of using hemoglobin HbA1c for diagnosing diabetes mellitus. Am J Med 2011;124(5):395-401. 6. Cowie CC, Rust KF, Byrd-Holt DD, Gregg EW, Ford ES, Geiss LS, et al. Prevalence of diabetes and high risk for diabetes using HbA1c criteria in the U.S. population in 1988-2006. Diabetes Care 2010;33(3):562-8. 7. Malkani S, DeSilva T. Controversies on how diabetes is diagnosed. Curr Opin Endocrinol Diabetes Obes 2012;19(2):97-103. 8. Colagiuri S, Lee CM, Wong TY, Balkau B, Shaw JE, Borch-Johnsen K, et al. Glycemic thresholds for diabetes-specific retinopathy: implications for diagnostic criteria for diabetes. Diabetes Care 2011;34(1):145-50. 9. McCance DR, Hanson RL, Charles MA, Jacobsson LT, Pettitt DJ, Bennett PH, et al. Comparison of tests for glycated haemoglobin and fasting and two hour plasma glucose concentrations as diagnostic methods for diabetes. BMJ 1994;308(6940):1323-8. 10. Cederberg H, Saukkonen T, Laakso M, Jokelainen J, Härkönen P, Timonen M, et al. Post-challenge glucose, HbA1c, and fasting glucose as predictors of type 2 diabetes and cardiovascular disease: a 10-year prospective cohort study. Diabetes Care 2010;33(9):2077-83. 11. Kramer CK, Araneta MR, Barrett-Connor E. HbA1c and diabetes diagnosis: the Rancho Bernardo Study. Diabetes Care 2010;33(1):101-3. 12. Bennett CM, Guo M, Dharmage SC. HbA(1c) as a screening tool for detection of type 2 diabetes: a systematic review. Diabet Med 2007;24(4):333-43. 13. Buell C, Kermah D, Davidson MB. Utility of HbA1c for diabetes screening in the 1999 2004 NHANES population. Diabetes Care 2007;30(9):2233-5. 14. Van‘t Riet E, Alssema M, Rijkelijkhuizen JM, Kostense PJ, Nijpels G, Dekker JM. Relationship between HbA1c and glucose levels in the general Dutch population: the new Hoorn Study. Diabetes Care 2010;33(1):61-6. 15. Herman WH, Cohen RM. Racial and ethnic differences in the relationship between HbA1c and blood glucose: implications for the diagnosis of diabetes. J Clin Endocrinol Metab 2012;97(4):1067-72. 16. Selvin E, Crainiceanu CM, Brancati FL, Coresh J. Short-term variability in measures of glycemia and implications for the classification of diabetes. Arch Intern Med 2007;167(14):1545-51. 17. Sato Y, Ohfusa H, Katakura M, Komatsu M, Yamada S, Yamauchi K, et al. A problem with the diagnosis of diabetes mellitus based on fasting plasma glucose. Diabet Med 2002;19(1):82-3. 18. Meigs JB, Muller DC, Nathan DM, Blake DR, Andres R; Baltimore Longitudinal Study of Aging. The natural history of progression from normal glucose tolerance to type 2 diabetes in the Baltimore Longitudinal Study of Aging. Diabetes 2003;52(6):1475-84. 19. Hare MJ, Shaw JE, Zimmet PZ. Current controversies in the use of haemoglobin HbA1c. J Intern Med 2012;271(3):227-36. 20. American Diabetes Association. Standards of medical care in diabetes—2012. Diabetes Care 2012;35(Supp 1):S11-63. 21. World Health Organization. Use of glycated haemoglobin (HbA1c) in the diagnosis of diabetes mellitus. Geneva, Switz: World Health Organization; 2011. 22. Canadian Task Force on Preventive Health Care. Recommendations on screening for type 2 diabetes in adults. CMAJ 2012;184(15):1687-96. 23. Rydén L, Standl E, Bartnik M, Van den Berghe G, Betteridge J, de Boer MJ, et al. Guidelines on diabetes, pre-diabetes, and cardiovascular diseases: executive summary. Eur Heart J 2007;28(1):88-136. Available from: http://eurheartjsupp.oxfordjournals.org/content/9/ suppl_C/C3/F5.large.jpg. Accessed 2012 Oct 23.
Tools for Practice articles in Canadian Family Physician (CFP) are adapted from articles published on the Alberta College of Family Physicians (ACFP) website, summarizing medical evidence with a focus on topical issues and practice-modifying information. The ACFP summaries and the series in CFP are coordinated by Dr G. Michael Allan, and the summaries are co-authored by at least 1 practising family physician and are peer reviewed. Feedback is welcome and can be sent to
[email protected]. Archived articles are available on the ACFP website: www.acfp.ca.
| Vol 59: january • janvier 2013
